<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    .triangle{
      /* 外部框使用非static定位，以便内部元素使用position: absolute; */
      position: relative;
      width: 100px;
      height: 100px;
    }
    .triangle span{
      /* position: absolute 方便任意定位 */
      position: absolute;
      /* 以block方式显示，以使得内联元素可自定宽高 */
      display: inline-block;
      background-color: red;
      height: 3px;
      top: 0;
      left: 3px;
      /* 设置z-index ，使得cricle置于其下 */
      z-index: 2;   
    }
    .triangle .first{
      width: 103px;
      /* 旋转90度 */
      transform: rotate(90deg);
      /* 设置旋转元素的基点位置 */
      transform-origin: 0 0;
    }

    
    .triangle .second{
      top:100px;
      width: 100px;
    }

    .triangle .third{
      transform: rotate(45deg);
      transform-origin: 0 0;
      width: 140px;
    }

    .circle {
      border: 1px solid blue;
      width: 50px;
      height: 50px;
      border-radius: 50px;
      background-color: blue;
      position: relative;
      top: -45px;
      left: 50px;
    }
  </style>
</head>
<body>
  <div class="triangle">
    <span class="first"></span>
    <span class="second"></span>
    <span class="third"></span>

  </div>
  <div class="circle">

  </div>
  
</body>
</html>